You can make computations on an irregular shaped region by defining a mask, as outlined in this FAQ. It shows one method of defining the mask based on variable values, but all that's needed is some method of generating a field on the same grid which is 1 where you want to work with data and missing otherwise:
Another tool is the pt_in_poly function. If what you have is a set of locations that defines the boundary, you could use that, and then define the mask from that.
On 5/5/2014 4:05 AM, Nitin Patil wrote: